System and method for building three-dimensional objects with metal-based alloys

ABSTRACT

A digital manufacturing system comprises a build chamber, a build platform disposed within the build chamber, at least one extrusion line configured to heat a metal-based alloy up to a temperature between solidus and liquidus temperatures of the metal-based alloy, a deposition head disposed within the build chamber and configured to deposit the heated metal-based alloy onto the build platform in a predetermined pattern, an umbilical having a first end located outside of the build chamber and a second end connected to the deposition head, and at least one gantry assembly configured to cause relative motion between the build platform and the deposition head within the build chamber, where the at least one gantry assembly comprises a motor disposed outside of the build chamber.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.12/145,131, filed on Jun. 24, 2008, and entitled “SYSTEM AND METHOD FORBUILDING THREE-DIMENSIONAL OBJECTS WITH METAL-BASED ALLOYS”, thedisclosure of which is incorporated by reference in its entirety.

BACKGROUND

The present invention relates to systems and methods for buildingthree-dimensional (3D) objects in digital manufacturing systems. Inparticular, the present invention relates to high-temperature,extrusion-based digital manufacturing systems for building 3D objectmetal-based alloys.

An extrusion-based digital manufacturing system (e.g., fused depositionmodeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) isused to build a 3D object from a computer-aided design (CAD) model in alayer-by-layer manner by extruding a flowable modeling material. Themodeling material is extruded through an extrusion tip carried by anextrusion head, and is deposited as a sequence of roads on a substratein an x-y plane. The extruded modeling material fuses to previouslydeposited modeling material, and solidifies upon a drop in temperature.The position of the extrusion head relative to the substrate is thenincremented along a z-axis (perpendicular to the x-y plane), and theprocess is then repeated to form a 3D object resembling the CAD model.

Movement of the extrusion head with respect to the substrate isperformed under computer control, in accordance with build data thatrepresents the 3D object. The build data is obtained by initiallyslicing the CAD model of the 3D object into multiple horizontally slicedlayers. Then, for each sliced layer, the host computer generates a buildpath for depositing roads of modeling material to form the 3D object.

In fabricating 3D objects by depositing layers of modeling material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of objects under construction, whichare not supported by the modeling material itself. A support structuremay be built utilizing the same deposition techniques by which themodeling material is deposited. The host computer generates additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the 3D object being formed. Support material is thendeposited from a second nozzle pursuant to the generated geometry duringthe build process. The support material adheres to the modeling materialduring fabrication, and is removable from the completed 3D object whenthe build process is complete.

A common interest of consumers in the industry of digital manufacturingis to increase the physical properties of the 3D objects, such as partstrengths and durability. One category of materials that could providesuch increased physical properties include metal-based alloys. Forexample, 3D objects built from high-strength metals may exhibit tensilestrengths that are substantially greater than those of industrialthermoplastic materials. However, the extrusion of metal-based alloysposes several issues for digital manufacturing. For example, theextrusion of metal-based alloys requires high operating temperatures,which may undesirably affect performance of current digitalmanufacturing systems. Furthermore, heating a metal-based alloy to atemperature above its liquidus temperature may prevent the alloy fromhaving a sufficient viscosity for extrusion, and may undesirably affectits grain structure upon re-solidification (e.g., dendrite formation).Thus, there is an ongoing need for systems and methods for build 3Dobjects from metal-based alloys with digital manufacturing techniques.

SUMMARY

An aspect of the disclosure is directed to a digital manufacturingsystem for building a three-dimensional object in a layer-by-layermanner. The system includes an enclosed, insulated build chamberconfigured to be purged of oxygen and to maintain one or moretemperatures of at least about 350° C. in at least a region ofdeposition, and a build platform disposed within the build chamber. Thesystem also includes a deposition head having an extrusion line and anextrusion tip. The extrusion line is configured to receive a feedstockof a metal-based alloy and to heat the metal-based alloy to atemperature between a solidus temperature and a liquidus temperature ofthe alloy. The extrusion tip is disposed within the build chamber, wherethe deposition head is configured to selectively deposit a flow of theheated metal-based alloy from the extrusion tip onto the build platformin a predetermined pattern.

Another aspect of the disclosure is directed to a digital manufacturingsystem for building a three-dimensional object in a layer-by-layermanner, where the system includes an enclosed, insulated build chamberconfigured to be purged of oxygen and to be maintained at one or moretemperatures of at least about 350° C. in at least a region ofdeposition. The system also includes a build platform disposed withinthe build chamber, and at least one extrusion line disposed outside ofthe build chamber and configured to receive a feedstock of a metal-basedalloy and to heat the metal-based alloy to a temperature between asolidus temperature and a liquidus temperature of the alloy. The systemfurther includes a deposition head having at least one extrusion tipdisposed in the build chamber, and a freeze valve assembly configured tocontrol the flow of heated metal-based alloy from one of the at leastone extrusion tip. The system further includes at least one coolantsolenoid disposed outside of the build chamber and configured toselectively relay a coolant to the freeze valve assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a digital manufacturing system for building 3Dobjects with metal-based alloys.

FIG. 2 is a front perspective view of a platform assembly and headassembly of the digital manufacturing system.

FIG. 3 is a top perspective view of the head assembly of the digitalmanufacturing system.

FIG. 4 is a bottom front perspective view of an x-y-axis gantry and anextrusion head of the digital manufacturing system.

FIG. 5 if an expanded partial sectional view of an extrusion line of theextrusion head for extruding a metal-based alloy.

FIG. 6 is a front perspective view of a first alternative extrusion headof the digital manufacturing system in use with an umbilical of thedigital manufacturing system, where the first alternative extrusion headhas a hybrid liquefier/freeze valve design.

FIG. 7 is a front perspective view of a second alternative extrusionhead of the digital manufacturing system in use with an umbilical of thedigital manufacturing system, where the second alternative extrusionhead has a hybrid liquefier/freeze valve design with multiple depositionlines.

FIG. 8 is a front perspective view of a third alternative extrusion headof the digital manufacturing system in use with an umbilical of thedigital manufacturing system, where the third alternative extrusion headhas a hybrid screw pump/freeze valve design.

FIG. 9 is an exemplary binary phase diagram of temperature versuscomposition for metal-based alloys that are suitable for use with thedigital manufacturing system.

FIG. 10 is a partial binary phase diagram of temperature versuscomposition for aluminum and silicon, illustrating the temperature phaseproperties of an exemplary metal-based alloy for use with the digitalmanufacturing system.

FIG. 11 is a micrograph of aluminum-silicon alloy wires prior to beingsubjected to extrusion temperatures.

FIG. 12 is a micrograph of the aluminum-silicon alloy wires after beingsubjected to an extrusion temperature between the solidus and liquidustemperatures of the alloy.

FIG. 13 is a micrograph of the aluminum-silicon alloy wires after beingsubjected to an extrusion temperature above a liquidus temperature ofthe alloy.

DETAILED DESCRIPTION

FIG. 1 is a front perspective view of system 10, which is ahigh-temperature, digital manufacturing system for building 3D objectswith metal-based alloys. As shown, system 10 includes housing 12 (shownwith broken lines), controller 13, build chamber 14, platform assembly16, head assembly 18, and quench tank 20. Housing 12 is the exteriorhousing of system 10, which protects the internal components of system10 from external conditions. System 10 also includes support frames (notshown) for retaining build chamber 14, platform assembly 16, and headassembly 18 within housing 12 at the respective locations shown inFIG. 1. Controller 13 is a computer-operated controller that receivessource geometries of 3D objects (e.g., CAD models in .STL formats), andconverts the received source geometries into sequences of processingsteps that system 10 performs to build the 3D objects. Accordingly,controller 13 provides control signals to system 10, and may be anintegral component of system 10 or external to system 10.

Build chamber 14 is an enclosed, high-temperature environment in which3D objects (represented as 3D object 22 in FIG. 1) are built with one ormore metal-based alloys. Build chamber 14 desirably functions as ahigh-temperature oven, and is desirably maintained at one or moreelevated temperatures to reduce the risk of mechanically distorting(e.g., curling) 3D object 22, and to decrease shrinkage due to thethermal expansion coefficient of the metal-based alloy. The temperatureof build chamber 14 may be elevated through the use of electrical and/orflame-based mechanisms using timed thermal ramping cycles.

The elevated temperature of build chamber 14 desirably ranges from thesolidification temperature of the metal-based alloy to the creeprelaxation temperature of the metal-based alloy. As used herein, theterm “creep relaxation temperature” of the metal-based alloy refers to atemperature at which the stress relaxation modulus of the alloy is 10%relative to the stress relaxation modulus of the alloy at thesolidification temperature of the alloy, where the stress relaxationmodulus is measured pursuant to ASTM E328-02. Examples of suitableelevated temperatures for build chamber 14 range from about 200° C. toabout 800° C., with particularly suitable temperatures ranging fromabout 400° C. to about 700° C., and with even more particularly suitabletemperatures ranging from about 500° C. to about 650° C.

The elevated temperature of build chamber 14 may also exhibit multipletemperature zones. For example, the temperature at the deposition sitemay be above the solidification temperature of the metal based alloy(e.g., below or about even with the creep relaxation temperature of themetal-based alloy), while the remainder of build chamber 14 may be belowthe solidification temperature of the metal based alloy (e.g., within20° C. below the solidification temperature of the metal based alloy).This prevents the temperature gradient within build chamber 14 fromgenerating significant stresses on 3D object 22 while cooling.

Furthermore, the elevated temperature within build chamber 14 isdesirably monitored with one or more process control loops to maintainthe desired temperature(s) during the build operations. Temperaturemonitoring is desirable in part because metal-based alloys typicallyhave high thermal conductivities, and therefore, radiate high amounts ofheat when cooling from the extrusion temperatures to the temperature ofbuild chamber 14.

Build chamber 14 is also desirably purged of oxygen (e.g., air) prior toa build operation, and may contain a non-oxidizing gas and/or vacuumconditions. For example, build chamber 14 may be vented to theatmosphere, and purged with an inert gas (e.g., nitrogen, helium, argon,and xenon). Additionally, build chamber 14 may be connected to a vacuumline (not shown) to reduce the pressure to vacuum conditions. Examplesof suitable vacuum pressures for performing the build operation includeabout 13 millipascals (about 10⁻⁴ Ton) or less, with more particularlysuitable pressures including about 1.3 millipascals (about 10⁻⁵ Torr) orless. The reduced pressure may also be used in combination with theinert gas. In embodiments in which inert gases are used, the atmospherewithin build chamber 14 is desirably re-circulated to maintaintemperature uniformity, and may be vented externally after the buildoperation is complete.

Build chamber 14 includes chamber walls 24, which are the lateral,ceiling, and base walls of build chamber 14, and are desirablyfabricated from one or more thermally-insulating materials capable ofwithstanding the elevated temperatures of build chamber 14. Suitablematerials for chamber walls 24 include heat-resistant and low-thermalexpansion materials, such as refractory ceramic firebricks, silicafirebricks, high-temperature alloys and superalloys, and combinationsthereof. Chamber walls 24 include access opening 26, which allows accesswithin build chamber 14 before and after build operations. Accessopening 26 is desirably secured with a door (not shown) during the buildoperations to maintain temperature uniformity within build chamber 14.

Platform assembly 16 includes drive motor 28, z-axis gantry 30, andbuild platform 32. Drive motor 28 is a motor (e.g., a direct-currentmotor) disposed outside of chamber walls 24 of build chamber 14, and isin signal communication with controller 13. Drive motor 28 is alsoengaged with z-axis gantry 30, which allows drive motor 28 to operatez-axis gantry 30 based on signals received from controller 13. Z-axisgantry 30 engages with drive motor 28 outside of build chamber 14, andextends through chamber walls 24 for retaining build platform 32. Asdiscussed below, z-axis gantry 30 is configured to move build platform32 along a vertical z-axis within build chamber 14 based on rotationalpower supplied by drive motor 28. Build platform 32 is a substrate onwhich 3D object 22 (and any corresponding support structure, not shown)is built, and is movably retained within build chamber 14 by z-axisgantry 30. Suitable materials for build platform 32 include materialscapable of use in the elevated temperature of build chamber 14, and thatare compatible with the metal-based alloy of 3D object 22. Examples ofsuitable materials for build platform 32 include nickel-based alloys andsuperalloys, graphites, ceramics, carbides (e.g., silicon carbides) andcombinations thereof.

Head assembly 18 includes drive motors 34 and 36, x-y-axis gantry 38,and extrusion head 40. Drive motors 34 and 36 are motors (e.g.,direct-current motors) disposed outside of chamber walls 24 of buildchamber 14, and are also in signal communication with controller 13.Drive motors 34 and 36 are also engaged with x-y-axis gantry 38, whichallows drive motors 34 and 36 to operate x-y-axis gantry 38 based onsignals received from controller 13. X-y-axis gantry 38 engages withdrive motors 34 and 36 outside of build chamber 14, and extends throughchamber walls 24 for retaining extrusion head 40. Extrusion head 40 isretained within build chamber 14, and is the portion of system 10 thatdeposits the metal-based alloy (and corresponding support material) in apredetermined pattern onto build platform 32 to build 3D object 22 (andcorresponding support structure) in a layer-by-layer manner.

As discussed below, x-y-axis gantry 38 is configured to move extrusionhead 40 in a horizontal x-y plane within build chamber 14 based onrotational power supplied by drive motors 34 and 36, where the x-axis,the y-axis (not shown in FIG. 1), and the z-axis are orthogonal to eachother. In an alternative embodiment, platform assembly 16 may beconfigured to move in the horizontal x-y plane within build chamber 14,and head assembly 18 may be configured to move along the verticalz-axis. Other similar arrangements may also be used such that one orboth of build platform 32 and extrusion head 40 are moveable relative toeach other, and such that the drive motors (e.g., drive motors 28, 34,and 36) are disposed outside of chamber walls 24 of build chamber 14.Positioning drive motors 28, 34, and 36 outside of chamber walls 24thermally isolates drive motors 28, 34, and 36 from the elevatedtemperature of build chamber 14. This reduces the risk of damaging drivemotors 28, 34, and 36, thereby preserving their operational lives. Inone embodiment, coolant gases (e.g., inert gases) are relayed to one ormore locations within housing 12 (outside of chamber walls 24) tofurther thermally isolate drive motors 28, 34, and 36 from the elevatedtemperature of build chamber 14.

During a build operation, build chamber 14 is substantially purged ofoxidizing gases (e.g., purging with argon and/or vacuum), and is thenheated to one or more elevated temperatures. Controller 13 then directsdrive motors 34 and 36 to move extrusion head 40 around within buildchamber 14 in the horizontal X-Y plane via x-y-axis gantry 38.Controller 13 also directs extrusion head 40 to extrude the metal-basedalloy onto build platform 32 in a pattern based on the movement ofextrusion head 40, thereby forming a layer of 3D object 22. As discussedbelow, the metal-based alloy is desirably heated to a semi-solid phaseof the alloy (i.e., between the solidus and liquidus temperatures). Thiscreates a slush-like consistency for the metal-based alloy, whichprovides a viscosity that is suitable for extrusion. As furtherdiscussed below, the metal-based alloy is also desirably kept below theliquidus temperature of the alloy to substantially preserve the grainstructure of the raw material alloy wire during deposition andre-solidification. This is beneficial for preserving the physicalproperties of the original grain structure of the metal-based alloy, andis particularly suitable for use with metal-based alloys that are heattreated prior to use with system 10.

When the layer is complete, the computer-operated controller thendirects drive motor 28 to lower build platform 32 along the z-axis by asingle layer increment via z-axis gantry 30. This allows the subsequentlayer of 3D object 22 to be built. These steps may then be repeateduntil 3D object 22 and any corresponding support structure are complete.After the build operation is complete, 3D object 22 may be stabilized toa uniform temperature prior to removal from build chamber 14 andimmersed into quench media. Quench tank 20 is a tank disposed outside ofhousing 12, and provides a fluid (e.g., warm water) to quench 3D object22 after the build operation. The quenching process is desirablyperformed within a short time period after 3D object 22 is thermallystabilized to prevent lower-temperature, solid solubility changes fromoccurring. This preserves the desired solid solution qualities of 3Dobject 22. Accordingly, quench tank 20 is desirably located adjacent tohousing 12 to allow 3D object 22 to be readily quenched after the buildoperation is complete. In one embodiment, quench tank 20 is alsodisposed in an inert gas atmosphere to further reduce the risk ofoxidizing 3D object 22 during the quenching process. After the quenchingprocess is complete, 3D object 22 may then undergo one or morepost-build operations (e.g., tempering and precipitation hardeningprocesses).

FIG. 2 is a front perspective view of platform assembly 16 and headassembly 18, where housing 12, controller 13, quench tank 20, 3D object22, and chamber walls 24 are omitted for ease of discussion. Thearrangement of platform assembly 16 and head assembly 18 reduces theexposure of temperature-sensitive components (e.g., drive motors 28, 34,and 36) to the elevated temperatures of build chamber 14 (shown in FIG.1). As shown in FIG. 2, z-axis gantry 30 of platform assembly 16includes drive pulley 42, drive belt 44, tensioner pulleys 46, idlerpulleys 48, and lead screws 50. Drive pulley 42 is a rotatable pulleythat is axially connected to drive motor 28, and relays rotational powerof drive motor 28 to drive belt 44. Drive belt 44 is a belt engaged withdrive pulley 42, tensioner pulleys 46, and idler pulleys 48, whichtransfers the rotational power of drive pulley 42 to idler pulleys 48.

Tensioner pulleys 46 are adjustable pulleys for tightening theengagement of drive belt 44 with drive pulley 42 and idler pulleys 48during assembly of z-axis gantry 30. Idler pulleys 48 are pulleys thatare axially engaged with lead screws 50, thereby allowing the rotationof idler pulleys 48 to correspondingly rotate lead screws 50. In theembodiment shown in FIGS. 1 and 2, drive pulley 42, drive belt 44,tensioner pulleys 46, and idler pulleys 48 are located outside ofchamber walls 24. As such, drive pulley 42, drive belt 44, tensionerpulleys 46, and idler pulleys 48 are also thermally isolated from buildchamber 14, and may be fabricated from a variety of materials (e.g.,metals, plastics, and ceramics). In an alternative embodiment, one ormore of drive belt 44, tensioner pulleys 46, and idler pulleys 48 may belocated within chamber walls 24, thereby exposing the components to thecomponents to the elevated temperature of build chamber 14. In thisembodiment, drive pulley 42, drive belt 44, tensioner pulleys 46, andidler pulleys 48 are desirably fabricated from materials capable of usein the elevated temperature of build chamber 14. For example, drive belt44 may be fabricated from one or more nickel-based alloys andsuperalloys, such as y′ (gamma prime) and y″ (gamma double prime)strengthened superalloys commercially available under the trademark“INCONEL” from Special Metals Corporation, New Hartford, N.Y. (e.g.,“INCONEL 718” alloy and “INCONEL 939” alloy).

Lead screws 50 are screws threadedly engaged with build platform 32 fortranslating the rotational motion of lead screws 50 into linear motionof build platform 32 along the vertical z-axis. During a buildoperation, controller 13 signals drive motor 28 to rotate drive pulley42 in a first rotational direction (represented by arrow 52). This pullsdrive belt 44 around drive pulley 42, tensioner pulleys 46, and idlerpulleys 48 in the same rotational direction as drive pulley 42(represented by arrow 53), thereby rotating idler pulleys 48 and leadscrews 50 in the same rotational direction. The rotation of lead screws50 causes build platform 32 to lower along the vertical z-axis(represented by arrow 54) due to the threaded engagement, untilcontroller 13 signals drive motor 28 to halt the rotation. Thisarrangement allows build platform 32 to be raised and lowered, whilealso thermally isolating drive motor 28 from build chamber 14.

As further shown in FIG. 2, head assembly 18 also includes umbilical 56,which is a double-tray baffle that extends through chamber wall 24 andconnects with extrusion head 40. Umbilical 56 is a thermally-insulativepathway that provides the metal-based alloy, support material, coolantair, and electrical connections to extrusion head 40, where the entranceof umbilical 56 (represented as entrance 57) is located outside ofchamber walls 24. Pressurized coolant air may also be relayed throughumbilical 56 to further reduce the temperature in the interior region ofumbilical 56, and the interior region of umbilical 56 is desirablymaintained at a temperature below about 200° C. to protect theabove-discussed components disposed within umbilical 56.

Umbilical 56 includes x-axis bellows 56 a and y-axis bellows 56 b, whichare metal-lined bellows that thermally isolate the interior region ofumbilical 56 from the elevated temperature of build chamber 14. Asshown, x-axis bellows 56 a is configured to curl along the x-axis inresponse to movement of extrusion head 40 along the x-axis. Similarly,y-axis bellows 56 b is the portion of umbilical 56 that connects toextrusion head 40, and is configured to curl along the y-axis inresponse to movement of extrusion head 40 along the y-axis. Thisdouble-tray arrangement for umbilical 56 allows extrusion head 40 tomove around in the horizontal x-y plane without substantial resistance,while also allowing umbilical 56 to retain a wall thickness that issufficient to thermally isolate the interior region of umbilical 56.

FIG. 3 is a top perspective view of head assembly 18, furtherillustrating the engagements between drive motors 34 and 36, x-y-axisgantry 38, extrusion head 40, and umbilical 56. As shown, x-y-axisgantry 38 includes x-axis guide rails 58, rail offsets 60, y-axis bridge62, x-axis belt mechanism 64, and y-axis belt mechanism 66. X-axis guiderails 58 are a first pair of rails that extend along the x-axis withinbuild chamber 14, and have opposing ends secured to rail offsets 60,where rail offsets 60 ensure that x-axis guide rails 58 maintain aparallel arrangement. In one embodiment, rail offsets 60 are secured tochamber walls 24 (shown in FIG. 1). Alternatively, x-axis guide rails 58may extend through chamber walls 24, such that rail offsets 60 aresecured to a support frame of system 10 within housing 12 (shown in FIG.1). Suitable materials for x-axis guide rails 58 include materialssuitable for use in the elevated temperature of build chamber 14 (shownin FIG. 1), such as graphite-metal blends commercially available underthe trademark “GRAPHALLOY” from Graphite Metallizing Corporation,Yonkers, N.Y.

Y-axis bridge 62 includes bearing sleeves 68 a and 68 b, and y-axisguide rails 70. Bearing sleeves 68 a and 68 b are support bearings thatare slidably retained by x-axis guide rails 58. This allows y-axisbridge 62 to slide along the x-axis. Suitable materials for bearingsleeves 68 a and 68 b include materials the have reduced friction withx-axis guide rails 58, and that are suitable for use in the elevatedtemperature of build chamber 14. Examples of suitable materials forbearing sleeves 68 a and 68 b include graphite-metal blends, such asthose discussed above for x-axis guide rails 58. Y-axis guide rails 70are a second pair of rails that extend along the y-axis within buildchamber 14, and have opposing ends secured to bearing sleeves 68 a and68 b. Suitable materials for y-axis guide rails 70 also includegraphite-metal blends, such as those discussed above for x-axis guiderails 58.

Extrusion head 40 includes bearing sleeves 72, which are supportbearings slidably retained by y-axis guide rails 70. This allowsextrusion head 40 to slide along the y-axis. Suitable materials forbearing sleeves 72 also include graphite-metal blends, such as thosediscussed above for x-axis guide rails 58.

X-axis belt mechanism 64 is the portion of x-y-axis gantry 38 thatengages with drive motor 34 to move y-axis bridge 62 along the x-axis.As shown, x-axis belt mechanism 64 includes drive pulley 74, drive belt76, and tensioner pulley 78. Drive pulley 74 is a rotatable pulley thatis axially connected to drive motor 34, and relays rotational power ofdrive motor 34 to drive belt 76. Drive pulley 74 is also located outsideof chamber walls 24. As such, drive pulley 74 is also thermally isolatedfrom build chamber 14, and may be fabricated from a variety of materials(e.g., metals, plastics, and ceramics).

Drive belt 76 is a metal belt engaged with drive pulley 74 and tensionerpulley 78, which allows the rotation of drive pulley 74 to rotate drivebelt 76. Suitable materials for drive belt 76 include those discussedabove for drive belt 44 (shown in FIG. 2), such as such as γ′ (gammaprime) and γ″ (gamma double prime) strengthened superalloys commerciallyavailable under the trademark “INCONEL” from Special Metals Corporation,New Hartford, N.Y. (e.g., “INCONEL 718” alloy and “INCONEL 939” alloy).

Tensioner pulley 78 is an adjustable pulley for tightening theengagement of drive belt 76 with drive pulley 74 during assembly ofx-axis belt mechanism 64. In the embodiment shown in FIGS. 1-3,tensioner pulley 78 is disposed within chamber walls 24, and is exposedto the elevated temperatures of build chamber 14. In this embodiment,tensioner pulley 78 is desirably fabricated from a material capable ofuse in the elevated temperature (e.g., high-temperature metals andceramics). In an alternative embodiment, drive belt 76 may extendthrough chamber walls 24 such that tensioner pulley 78 is secured to asupport frame of system 10 within housing 12.

As further shown in FIG. 3, drive belt 76 is secured to bearing sleeve68 b with fasteners 80. With this arrangement, the rotation of drivebelt 76 pulls y-axis bridge 62 along the x-axis based on the rotation ofdrive motor 34, thereby moving extrusion head 40 along the x-axis. Forexample, when drive motor 34 rotates drive pulley 74 in a firstrotational direction (represented by arrow 82), drive belt 76 rotatesaround drive pulley 74 and tensioner pulley 78 in the same rotationaldirection (represented by arrow 84). This correspondingly pulls y-axisbridge 62 along the x-axis in a direction that is away from drive motors34 and 36 (represented by arrow 86). Alternatively, when drive motor 34rotates drive pulley 74 in the opposing rotational direction to arrow82, drive belt 76 pulls y-axis bridge 62 along the x-axis in theopposing direction to arrow 86.

Y-axis belt mechanism 66 is the portion of x-y-axis gantry 38 thatengages with drive motor 36 to move extrusion head 40 along the y-axis.As shown, y-axis belt mechanism 66 includes drive pulley 88, drive belt90, tensioner pulleys 92, and idler pulleys 94 (a single idler pulley 94is shown in FIG. 3). Drive pulley 88 is a rotatable pulley that isaxially connected to drive motor 36, and relays rotational power ofdrive motor 36 to drive belt 90. As shown, drive pulley 78 is locatedoutside of chamber walls 24, and is thermally isolated from buildchamber 14. Drive belt 90 is a metal belt engaged with drive pulley 88,tensioner pulley 92, and idler pulleys 94, which allows the rotation ofdrive pulley 88 to pull drive belt 90 in the rotational direction ofdrive pulley 88. Suitable materials for drive belt 90 include thosediscussed above for drive belt 76.

Tensioner pulleys 92 are adjustable pulleys for tightening theengagement of drive belt 76 with drive pulley 74 during assembly ofx-axis belt mechanism 64. As shown, tensioner pulleys 92 are alsolocated outside of chamber walls 24, and are desirably fabricated frommaterials capable of withstanding the thermally-conductive contact withdrive belt 90. Idler pulleys 94 are rotatable pulleys axially secured tobearing sleeves 68 a and 68 b, and are engaged with drive belt 90. Asshown, idler pulleys 94 are located within chamber walls 24. As aresult, idler pulleys 94 are desirably fabricated from materials capableof use in the elevated temperature of build chamber 14 (e.g.,high-temperature metals and ceramics).

The ends of drive belt 90 (represented as belt ends 96) are secured to afixed surface (not shown), thereby preventing drive belt 90 from beingfully rotatable as discussed above for drive belt 44 (shown in FIG. 2)and drive belt 76. In one embodiment, chamber walls 24 (shown in FIG. 1)function as the fixed surface for retaining belt ends 96. Alternatively,drive belt 90 may extend through chamber walls 24, such that belt ends96 are secured to a support frame of system 10 within housing 12. Duringa build operation, drive motor 36 rotates drive pulley 88 in a firstrotational direction (represented by arrow 98), which pulls drive belt90 around drive pulley 88 and tensioner pulleys 92 in the samerotational direction (represented by arrow 100). As discussed below,this pulls extrusion head 40 along the y-axis, toward bearing sleeve 68a (represented by arrow 102). Alternatively, when drive motor 36 rotatesdrive pulley 88 in the opposing rotational direction to arrow 98, drivebelt 90 pulls extrusion head 40 along the y-axis in the opposingdirection to arrow 102.

FIG. 4 is a bottom front perspective view of x-y-axis gantry 38 andextrusion head 40, further illustrating the engagement between extrusionhead 40 and y-axis belt mechanism 66. As shown, idler pulleys 94 areaxially secured to bearing sleeves 68 a and 68 b of y-axis bridge 62,and y-axis belt mechanism 66 further includes idler pulleys 104 and 106axially secured to extrusion head 40 and engaged with drive belt 90. Asdiscussed above, belt ends 96 (shown in FIG. 3) of drive belt 90 aresecured to fixed locations. As such, rotation of drive pulley 88 (shownin FIG. 3) in the rotational direction of arrow 98 (shown in FIG. 3)pulls drive belt 90 in the rotational direction of arrow 100. Thiscorrespondingly reduces tension on idler pulley 104 and pulls idlerpulley 106 (and correspondingly extrusion head 40) in the direction ofarrow 102. Alternatively, if drive pulley 88 rotates in the opposingrotational direction to arrow 98, drive belt 90 is pulled in theopposing rotational direction to arrow 100, which reduces tension onidler pulley 106, and pulls idler pulley 104 (and correspondinglyextrusion head 40) in the direction of arrow 108 (i.e., opposite ofarrow 102). Accordingly, the use of x-y-gantry 28 allows extrusion head40 to be moved around the horizontal x-y plane within build chamber 14based on the control signals provided by controller 13 (shown in FIG.1).

As further shown in FIG. 4, extrusion head 40 also includes liquefierportion 110, which includes a pair of liquefiers and extrusion tips fordepositing the metal-based alloy and corresponding support material.Examples of suitable designs for extrusion head 40 and liquefier portion110 include those disclosed in LaBossiere, et al., U.S. PatentApplication Publication No. 2007/0003656, entitled “Rapid PrototypingSystem With Controlled Material Feedstock”; LaBossiere, et al., U.S.patent application Ser. No. 11/396,845, entitled “Single-Motor ExtrusionHead Having Multiple Extrusion Lines”; and Leavitt, U.S. patentapplication Ser. No. 11/888,076, entitled “Extrusion Head For Use InExtrusion-Based Layered Deposition System”, where the components arefabricated from materials suitable for use in the elevated temperatureof build chamber 14 (e.g., the materials discussed above for bearingsleeves 68 a and 68 b and drive belt 76. While liquefier portion 110 isshown with two liquefiers and extrusion tips, extrusion head 40 mayalternatively be configured to extrude a single material (i.e., oneliquefier and extrusion tip), or to extrude more than two materials(e.g., three to ten liquefiers and extrusion tips).

FIG. 5 is an expanded partial sectional view of extrusion line 112 ofextrusion head 40 (shown in FIGS. 1-4) for extruding the metal-basedalloy to build 3D object 22 (shown in FIG. 1). Extrusion line 112includes feed tube 114, coolant assembly 116, drive mechanism 118,liquefier assembly 120, and extrusion tip 122. Feed tube 114 receivesthe metal-based alloy in a wire form (represented as wire 124) from asupply source of wire 124 located external to build chamber 14 (shown inFIG. 1), where wire 124 is supplied to extrusion head 40 throughumbilical 56 (shown in FIGS. 2-4). The dimensions of wire 124 may varydepending on the metal-based alloy used, and on the dimensions andcapabilities of feed tube 114, drive mechanism 118, and liquefierassembly 120. Examples of suitable average diameters for wire 124 rangefrom about 0.508 millimeters (about 0.020 inches) to about 2.54millimeters (about 0.100 inches). In embodiments in which wire 124 issubstantially rigid due to the diameter, the radius of curvature of feedtube 114 (represented as radius 126) is desirably at least fifty timesthe diameter of wire 124 to reduce friction within feed tube 114.

Coolant assembly 116 includes duct portion 128 and porous sleeves 130,where duct portion 128 is a tube configured to relay a pressurizedcoolant gas to porous sleeves 130 from a supply source (not shown)located external to build chamber 14. Suitable coolant gases include theinert gases discussed above for build chamber 14 (e.g., argon). Poroussleeves 130 are a plurality of close-fitting, porous heat exchangersthat extend through the wall of feed tube 114. This allows the coolantgas supplied from duct portion 128 to form a high-shear gas film againstwire 124, thereby reducing the temperature of wire 124 prior to engagingwith drive mechanism 118.

The coolant gas supplied through coolant assembly 116 is desirably usedin addition to coolant gas flowing through umbilical 56, which assistsin thermally isolating the interior region of umbilical 56 from theelevated temperature of build chamber 14. In comparison, the coolant gasrelayed through coolant assembly 116 is desirably used to directly coolwire 124 prior to engagement with drive mechanism 118. The metal-basedalloy of wire 124 has a high thermal conductivity. As such, when wire124 resides in liquefier assembly 120 and is not presently beingextruded, the upstream portions of wire 124 adjacent to drive mechanism118 may heat up. This may soften the portions of wire 124 adjacent todrive mechanism 118, thereby potentially reducing the engagement betweendrive mechanism 118 and wire 124. Coolant assembly 116, however, lowersthe temperature of wire 124 adjacent to drive mechanism 118, whichpreserves engagement between drive mechanism 118 and wire 124.

Drive mechanism 118 includes drive roller 132 and idler roller 134,which are configured to engage and grip wire 124. Drive roller 132 isdesirably connected to a drive motor (not shown), which allows driveroller 132 and idler roller 134 to feed wire 124 into liquefier assembly120. In one embodiment, the drive motor for drive mechanism 118 isdisposed in extrusion head 40, and is thermally-isolated from buildchamber 14 by the coolant gas provided through umbilical 56.Alternatively, the drive motor for drive mechanism 118 may be locatedexternally to build chamber 14, and is interconnected with drive roller132 via gear and/or belt mechanisms that extend through umbilical 56.

Liquefier assembly 120 is the portion of extrusion head 40 that isdisposed in liquefier portion 110, and includes liquefier tube 136 andliquefier block 138. Liquefier tube 136 is a thin-wall, thermallyconductive tube extending through liquefier block 138, which has anentrance adjacent drive mechanism 118, and an exit at extrusion tip 122.In one embodiment, coolant gas is also supplied adjacent to the entranceof liquefier tube 136 to prevent the upstream portions of wire 124 fromheating up. Liquefier tube 136 provides a pathway for wire 124 to travelthrough liquefier block 138, and may include one or more inner-surfacecoatings to assist the flow of the metal-based alloy and to reduce therisk of chemical attacks between the metal-based alloy and liquefierassembly 120. Examples of suitable inner-surface coatings for liquefiertube 136 include carbide coatings, such as silicon carbides.Alternatively, liquefier tube 136 may be fabricated from stablematerials, such as graphites and ceramics.

Liquefier block 138 is a heating block for melting wire 124 to a desiredflow pattern based on a thermal profile along liquefier block 138. Dueto the high thermal conductivity of the metal-based alloy (relative tothermoplastic materials), the length of thermal profile along liquefierblock 138 may be reduced, which correspondingly reduces the flowresponse time during the build operation. Extrusion tip 122 is anextrusion tip secured to liquefier assembly 120, and has a tip diameterfor depositing roads of the metal-based alloy, where the road widths andheights are based in part on the tip diameter. Examples of suitable tipdiameters for extrusion tip 122 range from about 250 micrometers (about10 mils) to about 510 micrometers (about 20 mils). In one embodiment,extrusion tip 122 includes a non-wetting ring to reduce the risk of themetal-based alloy from building up outside of extrusion tip 122.

The metal-based alloy is extruded through extrusion line 112 ofextrusion head 40 by applying rotational power to drive roller 132 (fromthe drive motor). The frictional grip of drive roller 132 and idlerroller 134 translates the rotational power to a drive pressure that isapplied to wire 124. The drive pressure forces successive portions ofwire 124 into liquefier tube 136, where the metal-based alloy is heatedby liquefier block 138 to an extrudable state. As discussed below, theextrudable state is reached by heating the metal-based alloy to asemi-solid state of the metal-based alloy. This create a slush-likeconsistency for the metal-based alloy, which is suitable for extrusion.As further discussed below, in one embodiment, the metal-based alloy isheated to a temperature in the semi-solid state of the metal-based alloythat substantially preserves the original grain structure of wire 124upon cooling (e.g., substantially free of dendrites), which preservesthe physical properties of the original grain structure.

The unmelted portion of wire 124 functions as a piston with aviscosity-pump action to extrude the heated metal-based alloy throughliquefier tube 136 and extrusion tip 122, thereby extruding the heatedmetal-based alloy. The drive pressure required to force wire 124 intoliquefier tube 136 and extrude the metal-based alloy is based onmultiple factors, such as the resistance to flow of the metal-basedalloy, bearing friction of drive roller 132, the grip friction betweendrive roller 132 and idler roller 134, and other factors, all of whichresist the drive pressure applied to wire 124 by drive roller 132 andidler roller 134.

The metal-based alloy is deposited in a predetermined pattern to build3D object 22 in a layer-by-layer manner. As with extruded thermoplasticmaterials, the extrusion process of the metal-based alloy typicallyexhibits a self-planarization effect. This is due to the pressurefeedback, where the previously deposited alloy causes anupstream-directed pressure against the alloy being extruded fromextrusion tip 122. The pressure feedback is based on several factorssuch as cooling of the alloy being extruded by contact with thepreviously extruded and cooled alloy, back pressure from the alloybuilding up at extrusion tip 122, and changes in the effective timeconstant of liquefier assembly 120 due to constriction in extrusion tip122. This pressure feedback modifies the engagement between wire 124 anddrive roller 132/idler roller 134, which alters the extrusion rate ofthe metal-based alloy to induce the self-planarization effect. In analternative embodiment, a separate planarizer assembly (not shown) maybe incorporated into system 10 for providing an additional planarizingprocess for the layers or 3D object 22 and/or the corresponding supportstructure.

As discussed above, the temperature of build chamber 14 desirably allowsthe deposited metal-based alloy to cool to below the glass transitiontemperature of the alloy, thereby allowing the deposited alloy to retainits shape and support subsequently deposited layers. Moreover, theelevated temperature of build chamber 14 reduces the risk ofmechanically distorting the deposited metal-based alloy as it cools inbuild chamber 14, despite the high thermal conductivity of the alloy. Assuch, 3D object 22 may be built with the metal-based alloy of wire 124,which exhibits good physical properties, while also substantiallyretaining the same desired deposition patterns that are attainable withdeposited thermoplastic materials.

While extrusion head 40 is discussed above for a deposition process witha liquefier assembly, the extrusion line 112 may be replaced with avariety of different feedstock drive mechanism and liquefierarrangements. For example, system 10 may include one or more two-stagepump assemblies, such as those disclosed in Batchelder et al., U.S. Pat.No. 5,764,521; and Skubic et al., U.S. patent application Ser. No.12/069,536. This embodiment is beneficial for placing the drive motorsused to extrude the metal-based alloy outside of chamber walls 24,thereby thermally isolating the drive motors from the elevatedtemperature of build chamber 14. Alternatively, system 10 may includeone or more freeze valve assemblies, such as those disclosed inBatchelder et al., U.S. Pat. No. 6,578,596.

FIG. 6 is a front perspective view of extrusion head 140 in use withumbilical 56, where extrusion head 140 is an additional alternative toextrusion head 40 (shown in FIGS. 1-5) for use in system 10. Incomparison to extrusion head 40, which includes extrusion line 112(shown in FIG. 5), extrusion head 140 includes extrusion line 142,supply tube 144, coolant solenoid 146, coolant line 148, and freezevalve assembly 150. Accordingly, extrusion head 140 functions as ahybrid liquefier/freeze valve design where the metal-based alloy isheated to an extrudable state at extrusion line 142 and is depositedfrom freeze valve assembly 150.

Extrusion line 142 includes feed tube 154, coolant assembly 156, drivemechanism 158, liquefier assembly 160, and filter 162, where feed tube154, coolant assembly 156, drive mechanism 158, and liquefier assembly160 may function in the same manner as feed tube 114, coolant assembly116, drive mechanism 118, and liquefier assembly 120 of extrusion line112 (shown in FIG. 5). Extrusion line 142, however, is desirably locatedoutside of chamber walls 24 (shown in FIG. 1), thereby thermallyisolating extrusion line 142 from the elevated temperature of buildchamber 14. This is beneficial for protecting temperature-sensitivecomponents of extrusion line 142 (e.g., a drive motor for drivemechanism 158) from exposure to the elevated temperatures. Filter 162 isdisposed downstream from liquefier assembly 160 and is configured tofilter out residual impurities (e.g., oxides) carried by the heatedmetal-based alloy. Supply tube 144 extends through umbilical 56 andinterconnects extrusion line 142 and freeze valve assembly 150. Thus,supply tube 144 relays the heated metal-based alloy from extrusion line142 to freeze valve assembly 150.

Coolant solenoid 146 is also desirably located outside of build chamber14, and is a flow control apparatus configured to regulate the flow of acoolant gas to freeze valve assembly 150 via coolant line 148. Coolantsolenoid 146 includes gas inlet port 164, which is a port for receivinga pressurized coolant gas. Examples of suitable coolant gases for usewith coolant solenoid 146 include the inert gases discussed above forbuild chamber 14 (e.g., argon). This allows a single source of inert gasto be used to supply the inert gas for build chamber 14, the coolant gasfor umbilical 56, and the coolant gas for operating freeze valveassembly 150. Coolant solenoid 146 regulates the flow of the coolant gasto freeze valve assembly 150 (via coolant line 148) based on signalsprovided from controller 13 (shown in FIG. 1). Coolant line 148 extendsthrough umbilical 56, and interconnects coolant solenoid 146 and freezevalve assembly 150 for relaying the flow of coolant air from coolantsolenoid 146 to freeze valve assembly 150.

Freeze valve assembly 150 is a deposition assembly, such as thosedisclosed in Batchelder et al., U.S. Pat. No. 6,578,596, which isretained by an x-y-axis gantry (e.g., x-y-axis gantry 38, shown in FIGS.1-4) for movement around build chamber in the horizontal x-y plane.Freeze valve assembly 150 desirably includes a flow path tube (notshown), which has a high thermal resistance, for receiving anddepositing the heated metal-based alloy from supply line 144. When thecoolant gas from coolant line 148 is forced to flow around the outsideof the flow path tube, the coolant gas draws heat from the tube and themetal-based alloy at a heat transfer rate that is greater than the ratethat the tube is heated. This causes the tube to close, effectivelyblocking the flow of the metal-based alloy. When the flow of coolant gasis stopped (via coolant solenoid 146), the tube heats up and opens theflow path for the metal-based alloy. This allows the metal-based alloyto be deposited (represented by arrow 166) to form 3D object 22 (shownin FIG. 1) in a layer-by-layer manner.

Freeze valve assembly 150 is particularly suitable for use with themetal-based alloy due to the fast attainable response times. Forexample, the response time for operating freeze valve assembly 150 maybe below one millisecond, which is substantially less than the responsetimes attainable with thermoplastic materials (e.g., about 10milliseconds). Furthermore, the hybrid liquefier/freeze valve design ofextrusion head 140 allows the moveable components (e.g., coolantsolenoid 146 and drive mechanism 158) to be located outside of buildchamber 14, and reduces the number of temperature-sensitive componentswithin build chamber 14. This accordingly increases the operationallives of the components of system 10.

FIG. 7 is a front perspective view of extrusion head 168 and umbilical56, which illustrates an alternative to extrusion head 140 (shown inFIG. 6) for use in system 10. Extrusion head 168 functions in a similarmanner to extrusion head 140, and includes extrusion line 170, supplytube 172, solenoid assembly 174, coolant lines 176 a-176 c, and freezevalve assembly 178. Extrusion line 170 and supply line 176 function inthe same manner as extrusion line 142 and supply line 144 (shown in FIG.6) for relaying the heated metal-based alloy through umbilical 56 tofreeze valve assembly 178.

Solenoid assembly 174 includes coolant solenoids 174 a-174 c and gasinlet port 180, where each of coolant solenoids 174 a-174 c function inthe same manner as coolant solenoid 146 (shown in FIG. 6), and gas inletport 180 functions in the same manner as gas inlet port 164 (shown inFIG. 6). Accordingly, coolant solenoids 174 a-174 c regulate the flow ofthe coolant gases respectively through coolant lines 176 a and 176 c tofreeze valve assembly 178 based on signals provided from controller 13(shown in FIG. 1).

Freeze valve assembly 178 is a deposition assembly that functions in asimilar manner to freeze valve assembly 150 (shown in FIG. 6). However,in comparison to freeze valve assembly 150, which included a singledeposition line, freeze valve assembly 178 includes three separatedeposition lines for depositing the metal-based alloy supplied fromextrusion line 170. The three separate deposition lines are respectivelycontrolled by the regulated coolant gas flow from coolant solenoids 174a-174 c. This allows the metal-based alloy to be deposited in multiple,independent deposition lines (represented by arrows 182 a-182 c) to form3D object 22 (shown in FIG. 1) in a layer-by-layer manner.

While extrusion head 168 is discussed above as including a singleextrusion line (i.e., extrusion line 170), extrusion head 168 mayalternatively include multiple extrusion lines for supplying multiplematerials to freeze valve assembly 178. For example, extrusion head 168may include an extrusion line for each coolant solenoid of solenoidassembly 174, such as one or more extrusion lines for metal-based alloysand one or more extrusion lines for support materials. Furthermore,while solenoid assembly 174 is disclosed with three coolant solenoids(i.e., coolant solenoids 174 a-174 c), solenoid assembly 174 mayalternatively include a different number of coolant solenoids to depositmaterials from freeze valve assembly 178. Examples of suitable numbersof coolant solenoids for solenoid assembly 174 range from one (i.e.,coolant solenoid 146, shown in FIG. 6) to ten, with particularlysuitable numbers ranging about two to six, and with even moreparticularly suitable numbers ranging from two to four.

FIG. 8 is a front perspective view of extrusion head 184 and umbilical56, which illustrates an additional alternative to extrusion head 140(shown in FIG. 6) for use in system 10. Extrusion head 184 functions ina similar manner to extrusion head 140, and includes extrusion line 186,supply tube 188, coolant solenoid 190, coolant line 192, and freezevalve assembly 194. In this embodiment, coolant solenoid 190, coolantline 192, and freeze valve assembly 194 function in the same manner asdiscussed above for coolant solenoid 146, coolant line 148, and freezevalve assembly 150 of extrusion head 140 (shown in FIG. 6). Extrusionline 186, however, is used in lieu of extrusion line 142 (shown in FIG.6), where extrusion line 186 is a pump-based extrusion line thatincludes drive motor 196, coolant assembly 198, and liquefier assembly200.

Drive motor 196 is a motor connected to liquefier assembly 200, and isthermally isolated from liquefier assembly 200 via coolant assembly 198.Liquefier assembly 200 is a screw-pump liquefier that includes reservoir202, extrusion channel 204, screw 206, and vent 208. Reservoir 202 is achamber in which a supply of metal-based alloy (referred to as alloy210) is desirably heated to an extrudable state, and supplied toextrusion channel 204. Reservoir 202 also desirably includes layer 212(e.g., a graphite layer), which floats on the heated supply of alloy210. Layer 212 desirably reduces the risk of oxidation attacks on alloy210, and may also function as a thermally-insulating layer to retainheat within reservoir 202. Because the metal-based alloy is heated tothe extrudable state in reservoir 202, alloy 210 may be supplied toextrusion line 186 in a variety of media (e.g., powder, pellets, andwire).

Extrusion channel 204 is a channel for retaining screw 206, whichconnects to supply line 188. Screw 206 is an extrusion screw axiallyconnected to drive motor 196, and drives alloy 210 through extrusionchannel 204 to supply line 188. Vent 208 is a gas and liquid overflowvent, which reduces the risk of over-pressurizing extrusion channel 204during operation. During operation, alloy 210 is driven throughextrusion channel 204 and supply line 188 by the rotation of screw 206to freeze valve assembly 194. Freeze valve assembly 194 then extrudesthe heated metal-based alloy in response to the regulation flow ofcoolant air from coolant solenoid 190. This allows the metal-based alloyto be deposited (represented by arrow 214) to form 3D object 22 (shownin FIG. 1) in a layer-by-layer manner.

While extrusion head 184 is discussed above as including a singleextrusion line (i.e., extrusion line 186) and a single coolant solenoid(i.e., coolant solenoid 190), extrusion head 184 may alternativelyinclude multiple extrusion lines and/or multiple coolant solenoids forsupplying multiple materials to freeze valve assembly 194, as discussedabove for extrusion head 168 (shown in FIG. 7).

FIG. 9 is a binary phase diagram of temperature versus composition forexemplary metal A and metal B, which illustrates suitable metal-basedalloys for use with system 10 (shown in FIG. 1). All temperaturesreferred to herein are based on the pressure of build chamber 14 duringthe build operation (referred to as the “operating pressure”). Asdiscussed above, the operating pressure may be under vacuum orpartial-pressure conditions, pressurized with an inert gas aboveatmospheric pressure, or at atmospheric pressure with an inert gas.

As shown in FIG. 9, pure metal A (i.e., 0% by weight of metal B) has amelting temperature at T_(MA), and pure metal B (i.e., 100% by weight ofmetal B) has a melting temperature at T_(MB), where T_(MA) is higherthan T_(MB). Thus, pure metals A and B switch between solid and liquidphases respectively at T_(MA) and T_(MB). However, at compositionsbetween pure metals A and B, the metal-based alloys form a semi-solidphases between solidus curve 216 and liquidus curve 218. Below soliduscurve 216, a metal-based alloy only exists in solid phase, and aboveliquidus curve 218, the metal-based alloy only exists in the liquidphase. However, in the semi-solid phase the metal-based alloy consistsof solid crystals and liquid, thereby exhibiting a slush-likeconsistency.

For example, a metal-based alloy consisting of about 75% by weight metalA and about 25% of metal B has a solidus temperature T_(S) and aliquidus temperature T_(L). At temperatures below the solidustemperature T_(S), the metal-based alloy exists in a solid phase and isnot extrudable from system 10. Alternatively, at temperatures above theliquidus temperature T_(L), the metal-based alloy exists in a liquidphase. The liquid phase also is not suitable for extruding themetal-based alloy to build a 3D object. The viscosity of the metal-basedalloy in the liquid phase is not sufficient to retain its shape whendeposited onto build platform 32 (shown in FIGS. 1 and 2), and is alsonot sufficient to support subsequently deposited layers.

Between the solidus temperature T_(S) and the liquidus temperatureT_(L), however, the metal-based alloy exists in a semi-solid state,where the viscosity of the metal-base alloy decreases as the temperatureincreases from the solidus temperature T_(S) to the liquidus temperatureT_(L). Accordingly, the metal-based alloy may be heated in system 10 toa viscosity that is suitable for extrusion from extrusion head 40 (shownin FIGS. 1-4), extrusion head 140 (shown in FIG. 6), extrusion head 168(shown in FIG. 7), and/or extrusion head 184 (shown in FIG. 8). Examplesof suitable viscosities for extruding the metal-based alloys range fromabout 1 poise to about 1,000 poise, with particularly suitableviscosities ranging from about 5 poise to about 500 poise, and with evenmore particularly suitable viscosities ranging from about 10 poise toabout 100 poise.

Accordingly, suitable metal-based alloys for use with system 10 includeany alloy containing two or more metal elements and that exhibits atleast one semi-solid state (e.g., non-pure elements and non-eutecticalloys). Examples of suitable metal-based alloys includealuminum-silicon (AlSi) alloys, such as AlSi alloys including about 90%by weight to about 95% by weight aluminum, and about 5% by weight toabout 10% by weight silicon. Such alloys exhibit relatively low liquidustemperatures, and have suitable ranges between their solidus andliquidus temperatures for viscosity control. Examples of suitablecommercially available AlSi alloys include A356 and A357 casting alloys.

The suitable metal-based alloys are each desirably heated in system 10to a temperature that provides a suitable viscosity within thesemi-solid phase for extrusion. The metal-based alloys are desirably notheated above their liquidus temperatures during the processing withinsystem 10. Heating a metal-based alloy above its liquidus temperaturesand then cooling the alloy back down to its semi-solid phasesubstantially eliminates the original grain structure of the alloy, andforms dendrites upon cooling. Dendrite formation is also commonly foundin models fabricated by conventional casting techniques, and reduces thephysical properties of the metal-based alloy.

In contrast, the metal-based alloy used in system 10 is desirably heatedup to a temperature within the range of suitable viscosities forextrusion, and that also provides a high concentration of solid crystalsin the semi-solid phase. This substantially preserves the original grainstructure of the raw material alloy wire during deposition andre-solidification, and reduces the formation of dendrites. Furthermore,in one embodiment, the metal-based alloy is heated treated prior to usewith system 10. In this embodiment, the heat-treated, metal-based alloyis also heated up to a suitable temperature within the semi-solid phasefor extrusion. After being deposited in a layer-by-layer manner andres-solidified, the alloy substantially retains its originalheat-treated properties.

EXAMPLES

The present invention is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present inventionwill be apparent to those skilled in the art. Unless otherwise noted,all parts, percentages, and ratios reported in the following examplesare on a weight basis, and all reagents used in the examples wereobtained, or are available, from the chemical suppliers described below,or may be synthesized by conventional techniques.

An extrusion-based build operation was performed with analuminum-silicon (AlSi) alloy from an extrusion head to determine thefeasibility of attaining a semi-solid phase alloy having a viscositythat is suitable for extrusion. FIG. 10 is a partial binary phasediagram of temperature versus composition for aluminum and silicon,which illustrates the temperature phase profile for the AlSi alloy. TheAlSi alloy included about 93% by weight aluminum and about 7% by weightsilicon (i.e., AlSi Alloy A357), and had a solidus temperature of about575° C. and a liquidus temperature of about 620° C.

The metallographic structure of the AlSi alloy was substantially free ofdendrites, and exhibited silicon-particulate islands having an averagediameter of about 14 micrometers. The alloy was heated to a temperatureof about 610° C. and successfully extruded in a layer-by-layer manner toform a 3D object. An analysis of the AlSi alloy in the resulting 3Dobject showed that the AlSi alloy remained substantially free ofdendrites. As such, heating the AlSi alloy up to a temperature withinthe semi-solid phase of the alloy substantially preserved the originalgrain structure of the alloy. Furthermore, the use of the AlSi alloy wasalso beneficial for preventing hydrogen gettering, which typicallyoccurs at temperatures at or above about 650° C.

Sample metals wires consisting of the AlSi alloy were also heated toextrusion temperatures below and above the liquidus temperature of theAlSi alloy to determine the effect of the temperature on the grainstructure of the alloy. FIG. 11 is a micrograph of the AlSi alloy wiresprior to being subjected to the extrusion temperatures. The wires shownin FIGS. 11-13 were each embedded in epoxy, lapped back to approximatelythe axes of the rods, polished, and etched to assist in viewing thegrain structures of the alloys. As shown in FIG. 11, the AlSi alloyexhibited small average grain sizes, with evenly distributed siliconparticles.

A first set of the AlSi alloy wires were heated to an extrusiontemperature of about 610° C., which placed the AlSi alloys of the wiresin the semi-solid phase, for a duration of 30 minutes. FIG. 12 is amicrograph of the AlSi alloy wires after being heated up to thesemi-solid phase and re-solidified. As shown, the resulting AlSi alloywas free of dendrites, and the silicon particles melted to form smallconglomerates (about five silicon particles conglomerating into a singleconglomerate particle). Thus, the original grain structure of the alloywas substantially preserved.

A second set of the AlSi alloy wires were heated to a temperature abovethe liquidus temperature of the alloy (i.e., above about 620° C.), whichcompletely melted the alloy. FIG. 13 is a micrograph of the AlSi alloywires of Comparative Example A after being heated above the liquidustemperature and re-solidified. As shown, the resulting AlSi alloyexhibited large dendritic structures, which are typical in castings.Such dendritic structures can adversely affect the physical propertiesof the resulting alloys. In contrast, however, as shown in FIG. 12,heating the AlSi alloy up to a temperature that provides a viscositysuitable for extrusion, and that is within the semi-solid phase, allowsthe alloy to be extruded in a layer-by-layer manner to form a 3D object,where the resulting AlSi alloy of the 3D object substantially retainsits original grain structure.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A digital manufacturing system for building a three-dimensionalobject in a layer-by-layer manner, the system comprising: an enclosed,insulated build chamber configured to be purged of oxygen and tomaintain one or more temperatures of at least about 350° C. in at leasta region of deposition; a build platform disposed within the buildchamber; and a deposition head comprising: an extrusion line configuredto receive a feedstock of a metal-based alloy and to heat themetal-based alloy to a temperature between a solidus temperature and aliquidus temperature of the alloy; and an extrusion tip disposed withinthe build chamber, the deposition head being configured to selectivelydeposit a flow of the heated metal-based alloy from the extrusion tiponto the build platform in a predetermined pattern.
 2. The digitalmanufacturing system of claim 1, wherein the extrusion line comprises: adrive mechanism; and a liquefier assembly.
 3. The digital manufacturingsystem of claim 2, wherein the liquefier assembly comprises a heatedpathway fabricated from a material comprising graphite, a ceramicmaterial, or a combination thereof.
 4. The digital manufacturing systemof claim 2, wherein the liquefier assembly comprises a heating block anda graphite tube extending through the heating block.
 5. The digitalmanufacturing system of claim 2, wherein the system further comprises anumbilical having a first end located external to the build chamber and asecond end located within the build chamber, wherein the drive mechanismcomprises: a drive roller disposed in the deposition head; and a drivemotor located external to the build chamber and operably connected tothe drive roller through the umbilical.
 6. The digital manufacturingsystem of claim 1, wherein the feedstock of the metal-based alloycomprises a wire feedstock of the metal-based alloy, and wherein theextrusion line comprises: a liquefier assembly configured to heat themetal-based alloy; a drive mechanism configured to feed the wirefeedstock to the liquefier assembly; and a coolant assembly configuredto cool the wire feedstock prior to engagement with the drive mechanism.7. The digital manufacturing system of claim 6, wherein extrusion linefurther comprises a feed tube configured to supply the wire feedstock tothe drive mechanism, and wherein the coolant assembly comprises at leastone heat exchanger extending through the wall of the feed tube proximatethe drive mechanism, and a duct portion configured to relay apressurized coolant gas to the at least one heat exchanger.
 8. Thedigital manufacturing system of claim 1, wherein the build chamber isconfigured to exhibit multiple temperature zones, and wherein one of themultiple temperature zones in the region of deposition is configured tobe maintained at a temperature range from about 350° C. to about 700° C.9. A digital manufacturing system for building a three-dimensionalobject in a layer-by-layer manner, the system comprising: an enclosed,insulated build chamber configured to be purged of oxygen and to bemaintained at one or more temperatures of at least about 350° C. in atleast a region of deposition; a build platform disposed within the buildchamber; at least one extrusion line disposed outside of the buildchamber and configured to receive a feedstock of a metal-based alloy andto heat the metal-based alloy to a temperature between a solidustemperature and a liquidus temperature of the alloy; a deposition headcomprising: at least one extrusion tip disposed in the build chamber;and a freeze valve assembly configured to control the flow of heatedmetal-based alloy from one of the at least one extrusion tip; and atleast one coolant solenoid disposed outside of the build chamber andconfigured to selectively relay a coolant to the freeze valve assembly.10. The digital manufacturing system of claim 9, wherein the at leastone extrusion line comprises a liquefier assembly and a drive mechanism.11. The digital manufacturing system of claim 10, wherein the at leastone extrusion line further comprises a filter positioned downstream ofthe liquefier assembly and configured to filter out residual impuritiescarried by the heated metal-based alloy.
 12. The digital manufacturingsystem of claim 10, wherein the drive mechanism comprises a drive motorand the liquefier assembly comprises a screw-pump liquefier.
 13. Thedigital manufacturing system of claim 12, wherein the screw-pumpliquefier comprises a reservoir configured to heat the metal-basedalloy, an extrusion channel, a screw, and a vent, the reservoir having agraphite layer configured to prevent oxidation of the metal-based alloy.14. The digital manufacturing system of claim 10, wherein the liquefierassembly comprises heating block and a graphite tube extending throughthe heating block.
 15. The digital manufacturing system of claim 9, andfurther comprising a vacuum line configured to reduce the pressure inthe build chamber to vacuum conditions.
 16. The digital manufacturingsystem of claim 9, wherein the build chamber is configured to exhibitmultiple temperature zones, and wherein one of the multiple temperaturezones in the region of deposition is configured to be maintained at atemperature range from about 350° C. to about 700° C.
 17. The digitalmanufacturing system of claim 9, and further comprising athermally-isolating umbilical configured to channel the heated alloyfrom the at least one extrusion line to the freeze valve assembly. 18.The digital manufacturing system of claim 17, and further comprising aninert gas supply configured to supply an inert gas to the build chamber,the umbilical, and the coolant solenoid.
 19. The digital manufacturingsystem of claim 18, wherein the inert gas comprises nitrogen.
 20. Thedigital manufacturing system of claim 9, and further comprising a quenchtank configured to be disposed in an inert gas atmosphere for quenchingthe deposited alloy.